1. Field of the Invention
The present invention relates to an ejector cycle including an ejector. In the ejector cycle, a variable throttle is disposed upstream from a nozzle of the ejector, so that high-pressure refrigerant is decompressed in the variable throttle, before being decompressed in the nozzle.
2. Description of Related Art
In an ejector cycle, refrigerant is decompressed and expanded in a nozzle of an ejector so that gas refrigerant evaporated in an evaporator is sucked, and pressure of refrigerant to be sucked into a compressor is increased by converting expansion energy to pressure energy. In the nozzle of the ejector, the pressure energy of the refrigerant is converted to the speed energy thereof. Further, because refrigerant passing through the nozzle is decompressed to stride over the saturation liquid line, refrigerant boils near an inner wall surface defining a throttle portion of the nozzle. On the other hand, in a center portion separated from the inner wall surface, because refrigerant is difficult to boil, liquid drops of refrigerant are difficult to become minute. Therefore, nozzle efficiency and ejector efficiency may be decreased in the ejector cycle.
To overcome this problem, in JP-A-5-149652, a fixed throttle is disposed upstream from a nozzle in an ejector, so that refrigerant is decompressed by the fixed throttle and the nozzle in two steps. That is, refrigerant boils once in the fixed throttle at the first step, and the refrigerant is expanded at an inlet of the nozzle so as to boils in the nozzle at the second step while generating a bubble core. In the ejector, because the first throttle is the fixed throttle, a flow amount cannot be adjusted. Therefore, the nozzle efficiency and the ejector efficiency of the ejector cycle cannot be improved in a wide load variation area.